ES2426227T3 - Procedure and device for the precise detection of a contact between a rotating tool and a workpiece machined by the tool - Google Patents

Abstract

Device for the precise detection of a contact of a rotating tool (25) of machining with a piece (10) in a holder (11), the tool (25) being mounted on a spindle (22) mounted in a body ( 21) of an electro-borer (21), the spindle (22) being integral at its rear with a rotating shaft (24) and rotating at a rear (21 ') of the body (21) by means of bearings (27'), comprising the device a union of the part (10) and the body (21) to a first electrical potential, an electrical isolation of the tool (25) by means of insulating supports (23) and a device (30) for measuring an event related to electrical conduction between the tool (25) and the part (10), where an electric collector (27) connects the tool (25) to the measuring device (30) to effect a modification of an electrical event that occurs during contact on the measuring device of the tool (25) with the part (10), gift of the insulating supports (23) are arranged between the electro-mandrel shaft (24) and the body of the electormandrino (21) and are constituted by spindle bearings (22), characterized in that the manifold (27) is formed by a non-conductive bearing ( 27 ') provided in the shaft (24) of the electromagnet on the back of the spindle (22), the rear part (21') of the body being a conductive part and isolated from the rest of the body (21) by an insulator (29) and because the collector (27) is connected to an alternative voltage source by means of an impedance detector circuit (30) that receives information through the conductive part (21 ') and the bearing (27'), the approach taking place, which is characterized by the detection of a voltage variation measured between two points of the circuit.

Description

Procedure and device for the precise detection of a contact between a rotating tool and a workpiece machined by the tool

The present invention relates to the manufacture of parts with rotating tools, mainly machining electro-spinners that rotate at high speed.

From FR 2500776 or WO 97/30820, machining electrondrines are known. These machines are associated with control commands according to the classic axes of translation X, Y, Z and of rotation in A and B and, in general, allow an accuracy of the order of tens of micrometers, for example 30 micrometers, for machines of large dimensions (routes greater than 1.5 m).

In the framework of the continuation of a machining for a final finish and mainly during when the machining is resumed with a sister tool that can lead to problems in the repositioning of the spindle, it is desirable to improve the precision as much as possible and, therefore, it should be known as accurately as possible how the rotary tool approaches the part, also in case the rotation of the rotating tool and its high speed movement can cause axial displacements of the spindle.

Document US 2003/002943 provides a device for accurately detecting the approximation of the fixed tool in the type part where the modification of an event, mainly electrical or acoustic, is detected that occurs during the approach of the tool to the piece. However, this device uses a positive potential present in the entire structure of the machine.

From EP 1197819 a device is also known which has the characteristics of the preamble of the attached claim 1. The tool is insulated directly from the electro-mandrel shaft in which it is mounted by an insulating layer. The electrical information is collected by means not described in detail directly from the tool and which are probably of the type with brushes. This arrangement is probably satisfactory for rotating tools at low speed, but not so for tools working at high speeds such as those of the present invention. Indeed, the information collected by the brush collector is not reliable at high speed and, on the other hand, the isolation between the tool and the shaft leads to doubts about the exact position of the tool.

US 2006/0159537 describes a detector device where the information of change of electrical state is detected in the tool itself.

The invention aims to solve these problems and find a solution that allows a precise approximation, mainly for tools that rotate at high speed.

The invention achieves its objective by means of a device according to the attached claim 1.

Advantageously, the first potential is the earth, so that the body and the part and its part-holder are not carried to any potential, contrary to prior art devices.

According to a first embodiment, the manifold comprises an electrically conductive bearing, preferably of steel.

According to a first variant of the first embodiment, the collector is subjected to a second electrical potential by means of a current passage detector circuit that constitutes the measurement circuit, the contact being characterized by the detection of a change in the current passing in said circuit.

This change in the state of the current in the detector circuit may correspond to a binary change in current flow in the absence of current. For example, in a practical assembly with grounding (first zero potential), the card installed in the machine detects a lack of current in the measuring circuit: during the approach, the current

In practice, the part can be subjected to the first electrical potential (and mainly grounded) by means of the part-holder that is conductive and is subject to said first potential.

The great advantage of the invention is that the information of the electrical potential is captured in the back of the spindle, in the electromagnet shaft, in a part whose diameter is relatively small with the help of a bearing, conductor or non-conductor, relatively small dimensions. The rotation applied in a high speed machining is compatible with this arrangement.

The invention also relates to a precise approach procedure for a rotating tool for machining a part in a workpiece holder in which a device such as the one mentioned above is used.

According to an advantageous characteristic, in a first stage the tool is approached to a proximity of the piece and in a second stage the tool is advanced in very small steps detecting the approximation in the Other characteristics and advantages of the invention will become apparent from the following description of examples of embodiment and in relation to the attached figures, in which:

Figure 1: schematic view of a machine of machining of the electromandrino type and of the piece a

machining, as well as the electrical circuit associated with the procedure and a detector device that

It does not belong to the invention.

Figure 2: schematic view of a second machine of machining of the electromagnetic type and of the workpiece, as well as of the electrical circuit associated with the process and a detector device that does not belong to the invention, Figure 2A representing the electrical scheme corresponding to the configuration of these elements.

Figure 3: schematic view of a machine of machining of type electromandrino and of the piece a

machining, as well as the circuit associated with the procedure and the contact sensing device

according to the invention, Figure 3A representing the equivalent electrical circuit.

Figure 1 shows in a very simplified way a workpiece 10 placed on a thick plate 11 of electrical conductive material, for example of steel or cast iron.

The electromagnet 20 is represented in a simplified manner by its body 21 supported by a structure not traditionally represented, by rail, carriage and slider, where the relative displacements with respect to the piece are made by said support of the electromandrine and / or by the piece support according to 5 axes. The rotating spindle 22 is mounted at an appropriate point of the body 21 by means of a pair of non-conductive bearings 23, for example ceramic. At the rear of the spindle 22, the electromagnet shaft 24 rotates in the body 21, on bearings not shown in the figure. In the front part of the spindle 22, a location allows to receive the cone 25b of a rotating tool 25 for the removal of material intended to remove material from the piece 10, the tool having a collar 25a essentially the same size as the front part of the spindle 22 and rigidly supported on its cone by means of a tool adjustment system, not shown.

A control program directs the movements of the electromagnet 20 so that it forces the tip of the tool 25 to follow a predetermined path, first out of machining, the tool approaching the part and, once the precise approximation of the part has been made, in machining, where the tip of the tool effectively removes the material from the part, and finally outside the machining, when the tool moves away from the piece to be machined.

The invention relates more specifically to the final step of approaching the tool towards the part and the approach.

According to the invention, very precise means are provided for detecting the contact and, therefore, for the approach to the piece, based on the recognition of a modification in an electrical event when the tool comes into contact with the piece.

For this, the thick plate 11 is connected to ground by means of a cable 12 and the body 21 of the electromagnet is also connected to ground by means of a cable 26. The potential existing between the tool 21 and the spindle 22 is collected at the rear of the shaft of the electromagnet 24 by means of a mobile conductor 27 (a steel collector bearing) connected to a direct current source 28 through a current sensing circuit 30 capable of sending binary information about the passage or not of current.

When no current is detected in circuit 30, tool 25 and spindle 22 are still in an isolated state and, therefore, without contact with the part. On the contrary, a current detection represents an electrical continuity between the tool 25 and the part 10 and, therefore, that an approximation is produced.

According to the driving procedure of the tool of the invention, the spindle control circuit takes the tool to the immediate vicinity of the part according to a calculated path. Immediate proximity means a distance less than tenths of a millimeter, typically of the order of tenths of a millimeter, between the theoretical position of approach to the part and the tip of the tool, both in Z and XY. The approach includes the positioning of the rotary axes A and B.

Then, the rest of the route is carried out in very small steps, preferably of less than a few micrometers, typically of the order of micrometers, towards the theoretical approach position. In each step, the electrical conduction detected in circuit 30 is evaluated. The duration of the test is very short and if the test indicates that there is no conduction, the route for the next step is resumed, where said operations are repeated until the test point out that there is conduction and that the approach has been made. Therefore, the precision of the approximation results from the step selected for the test measurements, this is typically a micrometer. If each step requires Figure 2 represents a variant. It shows: the piece 10 in its conductive part holder 11 grounded by means of a cable 12; and the body 21 of the electromagnet 20 where the spindle 22 rotates with its shaft 24, rotating the tool 25 in rotation, the spindle 22 of the body 21 being isolated by insulating bearings 23, where the body is grounded with a cable 26, and a manifold 27 at the rear of the shaft 22. The manifold is connected to an alternative voltage source 28 through a measuring resistor 31. The spindle 22 isolated from the body 21 has an insulating impedance Zceb, while the tool 25 has with the piece 10 an impedance Zop, which is very high when the tool 25 does not touch the piece 10 and which is zero or close to zero when the tool touches the piece. In this way, the electric measuring circuit 30 represented in Figure 2A is created between these various elements, where the impedances Zceb and Zop are in parallel. By measuring the alternative voltage at the measuring resistor 31, a variation between the two states related to the impedance difference Zop is immediately detected.

The embodiment of Figure 3, which represents the invention, refers to the same elements 20, 21, 22, 23, 24, 25, 25a, 25b, 26, 28 as Figure 2, with the manifold 27 in the Part represented more precisely. The body 21 is extended at the rear by a conductive part 21 ', isolated from the main part 21 by an insulating layer 29. The spindle shaft 24 can rotate at the rear of the body 21' thanks to bearings 27 ', the which, in this embodiment and contrary to that of Figures 1 and 2, are insulators and are made of ceramic, for example. This function of insulating bearing is advantageously performed without major modifications, with the classic rotating joints for compressed air injection, spraying or irrigation through the center of the spindle. It is sufficient to electrically insulate said gasket with respect to the body 21 of the electromandrino (which is done here by the insulator 29). Circuit 30 receives the information through conductive part 21 ’and bearings 27’. Therefore, there is no conductivity between the sensor and the spindle, but a certain impedance. Figure 3A represents the circuit equivalent to Figure 3, where the impedance between the back piece 21 'and the body 21 is designated with Z1, with Z21 the impedance between the back piece 21' and the spindle shaft 24 and with Z22 the impedance between spindle shaft 24 and body 21. These three impedances are theoretically similar to ideal capacitors and are characterized by a certain frequency response. During the spindle approach, the impedance Z22 is short-circuited, which generates an electrical signal at the level of the equivalent circuit that is recovered via measurements 1 and 2.

A microprocessor analyzes the two measurements. Through a reinforced signal processing algorithm, it is able to detect the minimum contact between the tool and the part, while avoiding the detection of disturbances attributable to the system.

The microprocessor then sends a signal to the axis control that interrupts the approach.

To adapt to all types of machines, the microprocessor can be configured (optimum analysis frequency, sampling frequency, impedance variation detection threshold, buffer size for signal processing ...).

During use, the microprocessor acts as a source and analyzer. It does not send an alternative sinusoidal signal, but a 0-5V square signal.

The interest of the invention is illustrated by the following practical example:

As already noted, the invention is particularly intended for high speed machining, with a rotation speed of the order of 10,000 to 40,000 revolutions / min, using tool fixings of type HSK100

or HSK50 respectively. In a practical configuration, the outer diameter of the anterior bearing 23 may be 90 mm and its inner diameter 65 mm. If the fixation of the tool 25 is of type HSK 63, the collar 25b of the tool 25 is 63 mm, which, for a speed of 30,000 turns / min, implies a circumferential speed at the level of the collar 25a of 100 m / s.

According to the invention, the manifold located in the shaft 24 at the rear of the spindle allows using a manifold bearing of inner and outer diameter of 10 and 26 mm and, therefore, having a circumferential speed that remains reasonable despite the high tool speed

The invention allows to accurately detect the contact of the tool with the part. This precise detection can be used to detect the approach of the tool as described above. In an alternative use, damage to the tool can be detected based on the disappearance of the electrical signal for a tool with a cutting edge or a frequency change for a tool with several cutting edges not simultaneously introduced into the material.

In all embodiments, it may be appropriate to carefully clean the tools and the part in the approach area to remove dirt that could interfere with the recognition of the measured electrical events.

Claims (7)

1. Device for the precise detection of a contact of a rotating tool (25) of machining with a piece (10) in a holder (11), the tool (25) being mounted on a spindle (22) mounted in rotation in a body (21) of an electro-borer (21), the spindle (22) being integral at its rear with a rotating shaft (24) and rotating at a rear (21 ') of the body (21) by means of bearings (27 '), the device comprising a union of the part (10) and the body (21) to a first electrical potential, an electrical isolation of the tool (25) by means of insulating supports (23) and a measuring device (30) of an event linked to the electrical conduction between the tool (25) and the part (10), where an electric collector (27) connects the tool (25) to the measuring device (30) to effect a modification of said measuring device an electrical event that occurs during the contact of the tool (25) with l to piece (10), where the insulating supports (23) are arranged between the shaft (24) of the electromagnet and the body of the electormandrino (21) and are constituted by spindle bearings (22), characterized in that the manifold (27) is formed by a non-conductive bearing (27 ’) provided in the shaft (24) of the solenoid on the back of the spindle (22), the back (21 ’) of the body being a conductive piece and isolated from the rest of the body (21) by an insulator (29) and because the collector (27) is connected to an alternative voltage source by means of an impedance detector circuit (30) that receives information through the conductive part (21 ') and the bearing (27'), the approach taking place, which It is characterized by the detection of a measured voltage variation between two points of the circuit.

2.

Device according to claim 1, characterized in that the first potential is the earth.

3.

Device according to any of claims 1 or 2, characterized in that the part (10) is subjected to the first electrical potential by means of the part-holder (11) which is an electrical conductor.

Four.

Device according to any one of claims 1 to 3, characterized in that injection means for blowing compressed air through the spindle and the tool are provided.

5.

Device according to claim 4, characterized in that said injection means are constituted by a rotating joint that serves as a manifold (27).

6.

Accurate approach procedure of a rotating tool for machining a part in a workpiece holder, characterized in that a device according to any one of claims 1 to 5 is used.

7.

Method according to claim 6, characterized in that in a first stage the tool (25) is approached at an immediate proximity of the piece (10) and in a second stage the tool (25) is advanced by very small steps, detecting with the measurement circuit (30) the approximation, repeating one step each time an approximation is not detected, up to the approximation indicated by the measuring circuit.

 Measure 2 Measure 1 Measure